Scheduler Design

Overview

The scheduler is the core of Ved runtime.

It determines:

• execution order
• fairness
• system progression

Responsibilities

The scheduler:

• selects next message
• enforces deterministic ordering
• ensures fairness
• manages execution slices

Message Selection

Messages are ordered using:

(priority, logical_time, domain_id, sequence_id)

Selection Algorithm

function select_next_message(queue):
sort(queue, ordering_function)
return queue.pop_min()

Priority Handling

Priority influences execution order:

lower value → higher priority

aging adjusts priority over time

Aging Mechanism

To prevent starvation:

effective_priority = base_priority - aging_factor
id="rt-aging"

Queue Structure

Each domain maintains:

• mailbox queue
• pending message list

Scheduler aggregates:

• all domain queues

Fairness Guarantees

Scheduler ensures:

• every domain gets execution opportunity
• no indefinite postponement

Slice Management

Scheduler enforces:

• instruction limits per slice
• preemption and rescheduling

Quiescence Detection

Scheduler checks:

if all_queues_empty AND all_goals_satisfied: halt

Determinism Constraints

Scheduler must:

• avoid randomness
• maintain stable ordering
• use deterministic data structures